Photoresist features are measured using a scanning electron microscope (SEM) or other line width metrology device to determine if the desired feature size is within a specified range. The line width metrology device typically performs a single measurement, which specifies the size or scale at a single point on a feature's vertical wall. This process is often used in integrated circuit manufacturing before performing a patterning step, often a plasma etch, to determine the quality of the photo-lithographic process. If the quality is inadequate, the resist is stripped and the lithography is reworked.
As device features get smaller, this type of evaluation brought about by a scanning electron microscope or other line width metrology device becomes increasingly important. A reworking of lithography processes is costly and limits the efficient use of expensive equipment in semiconductor manufacturing.
Also, in the semiconductor industry, critical dimension metrology is used with the scanning electron microscope or other intensity trace to determine a width before and after an etching process. Typically, a specific algorithm is picked to determine where on the scanning electron microscope trace that forms an amplitude modulated waveform a position is used to determine the two edges that measure the critical dimension. This typically is an arbitrary method associated with increasingly poor predictive capabilities. For example, much of the method could be based on an inspector's intuition or experience. Thus, the predictive capabilities of the metrology are limited by the intuition and experience of the engineer or inspector making the algorithm determination. The predictive value of the comparison of line width between different technologies, fabrication plants and various companies in the industry are limited by the large variation and the choices of etch detection algorithms used by different metrologists in the industry.